The electroactive materials of electrodes of lithium ion batteries comprise at least one transition metal providing exchangeable valence electrons, said material also allowing insertion and removal or intercalation and deintercalation, respectively, of alkaline metal ions in order to keep neutrality of the material in case of exchange of valence electrons.
Some very interesting electroactive materials are not or not sufficiently conductive per se. Such materials are used in the form of microparticles (also termed microparticulate form) or nanoparticles (also termed nanoparticulate form) and in combination with a conductive matrix. Additional improvement is obtained if the particles are conductively coated.
It is assumed that conductive coatings add to the structural integrity of the particles because of improved regularity of electric field distribution on the surface of the particles and therewith connected improved structural integrity. In addition, even if the electroactive material particles are partially disintegrated over an extended number of cycles, the carbon coating proved advantageous. This may be due to encapsulation of the disintegrated particles and—if breaking apart—in partially conductively coated fragments. Methods for providing microparticles with a conductive coating are known. The preferred coating is a coating with carbonaceous material.
Carbon and carbonaceous materials are known as good electrical conductors and are already used to increase the electronic conductivity of electroactive materials. In general, carbon coating of oxide materials is carried out using a pyrolysis process that forms a thin layer of carbonaceous material such as pyrolitic graphite on the surface of particles provided that the electroactive core material is sufficiently stable in reducing atmosphere (see U.S. Pat. No. 6,962,666). According to U.S. Pat. No. 6,962,666, the carbonaceous coating may be obtained through thermal decomposition or through dehydrogenation, e.g. by partial oxidation of organic materials such as hydrocarbons and their derivatives like polycyclic aromatic moieties, sugars, carbon hydride and polymers. In some embodiments a lithium salt of carboxylic acids is used for simultaneous lithiation and pyrolytic carbonatious coating formation.
However, the problem with the coatings of the state of the art is that the pyrolysis reaction is not well defined. During pyrolysis, the hydrocarbon or carboxylic acid deposits may release compounds in different states of oxidation/reduction like hydrogen or water and carbon oxides or dioxides resulting in an inhomogeneous coating of not clearly defined composition and possibly in affected EAMs.
Thus, there is still a need for high energy storage materials with a good conductive coating and a method for obtaining such materials preferably in a one step reaction.